The present invention relates to a system for controlling decryption keys used for decrypting encrypted data. More particularly, the present invention relates to a system for controlling decryption keys used for decrypting encrypted data in a manner to permit disclosure of information to a plurality of users on a communication network at the same time.
In recent years, information can be readily exchanged among a plurality of terminals by way of a communication network such as the Internet. Among data to be exchanged, there is a kind of information with a property which requires that the information be kept secret up to a predetermined time at a predetermined date but be set free for disclosure afterward. An example of such information is confidential data of the government. In addition, such information is to be disclosed to a plurality of users after the predetermined time at the predetermined date. In other words, there must be an assurance that information can be put in a state that allows a plurality of users to know the most essential part of the information. An example of information with such a property is information on a transaction such as a tender or an offer.
For such information, there has been provided a conventional method whereby information produced at a terminal of an information producer is kept at the terminal up to a date or a time of a date at which protection of the confidentiality of the information is ended. It is not until the termination of the confidentiality protection is ended, that is, the expiration of the time of the confidentiality protection, that the information is disclosed and distributed to a plurality of users.
With the method described above, however, it is not easy for an information producer to disclose or distribute information to a plurality of users at the same time with a high degree of reliability. Particularly if the amount of the information to be disclosed or distributed is large or if there are a large number of users on the distribution list.
In addition, the information producer has to control the date & time at which information is to be disclosed or distributed. In particular, if there are many kinds of information to be disclosed or distributed at the same date & time, it will be difficult to assure that these pieces of information will be disclosed or distributed to a plurality of users simultaneously.